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23.
AWSのドキュメントをよく読む
Ephemeral Ports
The example network ACL in the preceding section uses an ephemeral port range of
49152-65535. However, you might want to use a different range for your network
ACLs. This section explains why.
The client that initiates the request chooses the ephemeral port range. The range
varies depending on the client's operating system. Many Linux kernels (including
the Amazon Linux kernel) use ports 32768-61000. Requests originating from Elastic
1024-65535
Load Balancing use ports
. Windows operating systems through
Windows Server 2003 use ports 1025-5000. Windows Server 2008 uses ports 4915265535. Therefore, if a request comes in to a web server in your VPC from a Windows
XP client on the Internet, your network ACL must have an outbound rule to enable
traffic destined for ports 1025-5000.
If an EC2 instance in your VPC is the client initiating a request, your network
ACL must have an inbound rule to enable traffic destined for the ephemeral ports
specific to the type of instance (Amazon Linux, Windows Server 2008, and so on.).
In practice, to cover the different types of clients that might initiate traffic
to public-facing instances in your VPC, you need to open ephemeral ports
1024-65535. However, you can also add rules to the ACL to deny traffic on
any malicious ports within that range. Make sure to place the DENY rules earlier
in the table than the rule that opens the wide range of ephemeral ports.

27.
Note: Network ACLs are stateless, which means
for any given request you want to handle, you
must create rules in both directions. For
example, to handle inbound traffic to a web
server in your VPC, you must allow both
inbound TCP port 80, and outbound TCP ports
1024-65535.